1. Field of the Invention
The present invention relates to a disk-shaped magnetic recording medium that is rotatably housed in a small magnetic disk cartridge.
2. Description of the Related Art
To record or reproduce information, a recording medium is removably loaded in the card slot of electronic equipment such as a digital still camera, a digital video camera, a laptop personal computer (PC), etc. Examples of such recording media that have been put to practical use are a semiconductor memory type, a hard disk type, an optical disk type, a magnetic disk type (e.g., a floppy disk type), etc.
Among these recording media, semiconductor memories are most widely used because they are easy to handle and have a relatively large recording capacity. However, they are relatively expensive. Because of this, in digital cameras employing the semiconductor memory, the photographed image data is transferred to a PC and stored, the data is deleted from the memory, and the semiconductor memory is repeatedly used.
Although there are hard disks that can store 340 megabytes (MB) of data or 1 gigabyte (GB) of data, they are also expensive. Because of this, data is transferred to another device and stored, and hard disks are repeatedly used.
Optical disks have a large recording capacity for their size. For example, an optical disk with a size of 35 mm×41 mm×11 mm can store 256 MB of data. Optical disks with a recording capacity of 512 MB are about to be realized. However, optical disks have the disadvantage that the recording speed is slow, because the writing time is time-consuming.
Meanwhile, there are known some magnetic disks (e.g., floppy disks) of a small size of 50 mm×55 mm×2 mm. Such a small magnetic disk can be exchangeably loaded in a disk drive of a size that can be inserted into the card slot of a PC, etc. However, the recording capacity is as small as 40 MB and insufficient to record image data photographed by a camera. In addition, the size is not suitable for digital cameras.
With the spread of PCs, digital cameras have spread rapidly in recent years because of the simplicity of recording, enhancement in picture quality due to the development of imagers, possibility of data deletion and transmission, recording capacity size, etc. However, the method of use is restricted, because recording media are limited in cost and recording capacity, as described above. For instance, since recording media are very expensive, a single camera has only a single recording medium, which is repeatedly used. That is, when the recording medium is filled with data, the data is transferred to a PC and deleted from the recording medium as described above. Because of this, there are cases where the recording medium is filled up during a trip. In addition, the recording medium cannot be stored as is, containing data therein, nor can it be given away to a person.
Hence, there is a demand for realization of a recording medium which is large in recording capacity, low in cost, and small in size so that the data photographed by a digital camera can be stored as is or given away to a person. In PCs, there is also a demand for realization of a recording medium which is large in recording capacity, low in cost, and small in size so that the medium with stored data can be handed to a person.
To meet the aforementioned demands, it is contemplated that the above-described inexpensive small large-capacity recording medium may comprise a card-type disk drive which is loaded in electronic equipment such as a PC and a digital camera, and a magnetic disk cartridge which is loaded in the small disk drive. That is, it is contemplated that such a magnetic disk cartridge may include a housing in which a flexible magnetic disk capable of high-density recording is rotatably housed, and have a recording capacity of 200 MB or larger. Examples of magnetic recording media with a high recording density are a recording medium with a thin metal film formed by vapor deposition, a recording medium with a thin metal film formed by sputtering, and a recording medium employing barium ferrite powder or ferromagnetic magnetic powder. An example of a magnetic recording medium with a high recording density employing barium ferrite powder is disclosed in U.S. patent application Ser. No. 10/266,584.
The “magnetic recording medium with a high recording density employing barium ferrite powder” is a magnetic disk containing barium ferrite powder in its magnetic layer, and employs a material capable of a high recording density. The magnetic disk may comprise a magnetic recording medium disclosed. The magnetic recording medium has a non-magnetic layer which includes both non-magnetic powder and a binder, and a magnetic layer which includes both ferromagnetic powder (which is ferromagnetic metal powder or hexagonal-system ferrite powder) and a binder. The non-magnetic layer and the magnetic layer are formed on at least one surface of a non-magnetic substrate in the recited order. In the non-magnetic layer, the quantity of carbon black whose average particle diameter is 10 to 30 nm is 10 to 50 weight parts with respect to 100 weight parts of the aforementioned non-magnetic powder. The thickness of the magnetic layer is 0.2 μm or less. According to a microanalysis by an electron beam, the standard deviation (b) of the strength of an element with respect to an average strength (a) resulting from ferromagnetic powder is 0.03≦b/a≦0.4. The center plane average roughness Ra of the magnetic layer is 5 nm or less, and the 10-point average roughness Rz is 40 nm or less. In a magnetic disk employing the above-described material, information is recorded or reproduced by a magnetic head such as an MR head capable of a high recording density.
The above-described magnetic recording medium can realize a recording capacity of 200 MB or larger, preferably 500 MB or larger. Therefore, if a still image has 1 MB of data 500 MB or larger. Therefore, if a still image has 1 MB of data per image, the magnetic recording medium can store 500 images. In the case of a motion picture, the magnetic recording medium can store image contents of about 30 minutes. Thus, the magnetic recording medium can store a motion picture photographed by a digital camera or a motion picture transmitted by a portable telephone. As a result, users can conveniently use the magnetic recording medium. Furthermore, the magnetic recording medium can be conveniently used in PCs as an inexpensive large-capacity recording medium. Thus, the convenience is great.
Card-type disk drives are employed in electronic equipment such as PCs, digital cameras, etc. In the case of PCs, as shown in FIG. 5A, a disk drive 6 is connected electrically with the socket 4 of a card 2 that is inserted in the card slot of a PC. In the case of small electronic equipment such as a digital camera 3 shown in FIG. 5B, a disk drive 6 is connected electrically with the socket of the receiving portion 5 of the camera 3. Therefore, the disk drive 6 is extremely small in size and has, for example, a length of 38 to 55 mm, a width of 35 to 51 mm, and a thickness of 3 to 5 mm. A magnetic disk cartridge 8 is inserted into the disk drive 6 through a slot formed in the disk drive 6, and has, for example, a length and a width of 25 to 36 mm and a thickness of 1 to 3 mm.
To achieve the above-described high recording density, it is necessary that a magnetic head touch the magnetic recording medium stably. In the case where a flexible recording sheet is employed as the magnetic recording medium, the gap between the magnetic sheet and the magnet head varies due to the so-called flutter of the magnetic sheet being rotated. Because of this, there is a problem that recording-reproduction characteristics will degrade. With a reduction in the pitch between recording tracks, there is another problem that the position of a recording track in the radial direction of the disk will be slightly shifted or fluctuated.